[CMake] Check AV_EIGEN_MEMORY_ALIGNMENT when building dependencies

This way dependencies use the same Eigen alignment settings as
AliceVision itself.

CMakeLists.txt

@@ -231,11 +231,29 @@ ExternalProject_Add(${TBB_TARGET}
 #
 set(TBB_CMAKE_FLAGS -DTBB_INCLUDE_DIRS:PATH=${CMAKE_INSTALL_PREFIX}/include -DTBB_LIBRARIES=${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}/libtbb.so)
 
+# Eigen requires overaligned buffers for maximum efficiency (e.g. on AVX512 buffers may need to
+# be aligned to 64 bytes). AliceVision currently does not support this. Fortunately this is fixed
+# in C++17. While we can't upgrade to C++17 just yet, some compilers support overaligned
+# allocation feature with a separate flag, so use it if alignment is enabled in Eigen.
+# See https://eigen.tuxfamily.org/dox/group__TopicUnalignedArrayAssert.html
+if(AV_EIGEN_MEMORY_ALIGNMENT)
+  if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 7.1)
+    set(EIGEN_CMAKE_ALIGNMENT_FLAGS "-DCMAKE_CXX_FLAGS:STRING=-faligned-new")
+  elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 6.0)
+    set(EIGEN_CMAKE_ALIGNMENT_FLAGS "-DCMAKE_CXX_FLAGS:STRING=-faligned-new")
+  elseif(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 19.12)
+    set(EIGEN_CMAKE_ALIGNMENT_FLAGS "-DCMAKE_CXX_FLAGS:STRING=/Zc:alignedNew")
+  else()
+    message(FATAL_ERROR "AV_EIGEN_MEMORY_ALIGNMENT is only supported starting GCC 7.1, Clang 6.0 and MSVC 2017 15.5")
+  endif()
+else()
+  set(EIGEN_CMAKE_ALIGNMENT_FLAGS
+      "-DCMAKE_CXX_FLAGS:STRING=-DEIGEN_MAX_ALIGN_BYTES=0 -DEIGEN_MAX_STATIC_ALIGN_BYTES=0"
+      "-DCMAKE_C_FLAGS:STRING=-DEIGEN_MAX_ALIGN_BYTES=0 -DEIGEN_MAX_STATIC_ALIGN_BYTES=0")
+endif()
+
 # Add Eigen
 set(EIGEN_TARGET eigen)
-set(EIGEN_DISABLE_ALIGN_FLAGS
-    "-DCMAKE_CXX_FLAGS:STRING=-DEIGEN_MAX_ALIGN_BYTES=0 -DEIGEN_MAX_STATIC_ALIGN_BYTES=0"
-    "-DCMAKE_C_FLAGS:STRING=-DEIGEN_MAX_ALIGN_BYTES=0 -DEIGEN_MAX_STATIC_ALIGN_BYTES=0")
 ExternalProject_Add(${EIGEN_TARGET}
        URL https://gitlab.com/libeigen/eigen/-/archive/3.4.0/eigen-3.4.0.tar.bz2
        URL_HASH MD5=132dde48fe2b563211675626d29f1707
@@ -247,10 +265,17 @@ ExternalProject_Add(${EIGEN_TARGET}
        SOURCE_DIR ${CMAKE_CURRENT_BINARY_DIR}/eigen
        BINARY_DIR ${BUILD_DIR}/eigen_build
        INSTALL_DIR ${CMAKE_INSTALL_PREFIX}
-       CONFIGURE_COMMAND ${CMAKE_COMMAND} ${CMAKE_CORE_BUILD_FLAGS} ${EIGEN_DISABLE_ALIGN_FLAGS} -DCMAKE_INSTALL_PREFIX:PATH=<INSTALL_DIR> <SOURCE_DIR>
+       CONFIGURE_COMMAND ${CMAKE_COMMAND} ${CMAKE_CORE_BUILD_FLAGS} ${EIGEN_CMAKE_ALIGNMENT_FLAGS} -DCMAKE_INSTALL_PREFIX:PATH=<INSTALL_DIR> <SOURCE_DIR>
        BUILD_COMMAND $(MAKE) -j${AV_BUILD_DEPENDENCIES_PARALLEL}
        )
-set(EIGEN_CMAKE_FLAGS ${EIGEN_DISABLE_ALIGN_FLAGS} -DEigen3_DIR:PATH=${CMAKE_INSTALL_PREFIX}/share/eigen3/cmake -DEIGEN3_INCLUDE_DIR=${CMAKE_INSTALL_PREFIX}/include/eigen3 -DEIGEN_INCLUDE_DIR=${CMAKE_INSTALL_PREFIX}/include/eigen3 -DEigen_INCLUDE_DIR=${CMAKE_INSTALL_PREFIX}/include/eigen3)
+
+set(EIGEN_CMAKE_FLAGS
+    ${EIGEN_CMAKE_ALIGNMENT_FLAGS}
+    -DEigen3_DIR:PATH=${CMAKE_INSTALL_PREFIX}/share/eigen3/cmake
+    -DEIGEN3_INCLUDE_DIR=${CMAKE_INSTALL_PREFIX}/include/eigen3
+    -DEIGEN_INCLUDE_DIR=${CMAKE_INSTALL_PREFIX}/include/eigen3
+    -DEigen_INCLUDE_DIR=${CMAKE_INSTALL_PREFIX}/include/eigen3
+    )
 
 if(AV_BUILD_OPENGV)
 set(OPENGV_TARGET opengv)